1. Technical Field
The present disclosure relates to a variable nozzle unit which adjusts a passage area (flow rate) of an exhaust gas to be supplied to a turbine wheel side in a variable geometry system (VGS) turbocharger and a variable geometry system turbocharger.
2. Description of the Related Art
The variable geometry system turbocharger is a turbocharger having a variable nozzle unit installed in a turbine housing. In recent years, various kinds of development have been made for this variable nozzle unit (refer to Japanese Patent Application Laid-Open Publication Nos. 2009-243431 (Patent Literature 1) and 2009-243300 (Patent Literature 2)).
The conventional variable nozzle unit includes a first nozzle ring as an annular first wall member and a second nozzle ring as an annular second wall member, installed in the turbine housing. The first nozzle ring is provided concentrically with the turbine wheel. Furthermore, the second nozzle ring is provided at a position separated in an axial direction (an axial direction of the turbine wheel) with respect to the first nozzle ring. The second nozzle ring is provided integrally with the first nozzle ring by a plurality of connecting pins aligned at intervals in a circumferential direction (a predetermined circumferential direction).
The first nozzle ring has a surface (a facing surface) facing the second nozzle ring. The second nozzle ring has a surface (a facing surface) facing the first nozzle ring. A plurality of variable nozzles is provided between these facing surfaces. The variable nozzles are provided at equal intervals in the circumferential direction (the predetermined circumferential direction). Each of the variable nozzles is rotatable in a forward direction and in a reverse direction (an opening direction and a closing direction) around a shaft core parallel to a shaft core of the turbine wheel. Furthermore, a link chamber is defined on a surface side opposite to the facing surface of the first nozzle ring. A link mechanism is provided in the link chamber. The link mechanism synchronously rotates the plurality of variable nozzles in the forward direction or in the reverse direction. When the plurality of variable nozzles is synchronously rotated in the forward direction (opening direction), the passage area (throat area) of the exhaust gas supplied to the turbine wheel side becomes larger. When the plurality of variable nozzles is synchronously rotated in the reverse direction (closing direction), the passage area of the exhaust gas becomes smaller.
A support ring is provided on the surface side opposite to the facing surface of the first nozzle ring. An outer diameter of the support ring is larger than an outer diameter of the first nozzle ring. An inner edge portion of the support ring is connected to one end portions of the plurality of connecting pins connecting the first nozzle ring and the second nozzle ring. Accordingly, the support ring is connected integrally to the first nozzle ring and the second nozzle ring. An outer edge portion of the support ring is attached to a bearing housing in a state of being sandwiched by the bearing housing and the turbine housing.